In Release 12, the 3GPP Long Term Evolution (LTE) standard has been extended to support device to device (D2D) communications (specified as “sidelink” communications). D2D communication targets both commercial and public safety applications. The D2D support in Rel-12 LTE enables device discovery, in which devices are able to sense the proximity of other devices and associated applications by broadcasting and detecting discovery messages that carry device and application identities. Another aspect of D2D enables direct communication between devices using physical channels terminated directly by the devices.
One of the potential extensions for the device-to-device functionality consists of support of vehicle-to-anything (V2x) communication, which includes any combination of direct communication between vehicles, pedestrians and/or infrastructure. V2x communication may take advantage of a network infrastructure, when available, but at least basic V2x connectivity may be possible even when network coverage is unavailable. Providing an LTE-based V2x interface may be economically advantageous because of the LTE economies of scale, and because it may enable tighter integration between communications with the network infrastructure (V2I) and vehicle-to-pedestrian (V2P) and vehicle-to-vehicle (V2V) communications, as compared to using a dedicated V2x technology.
An example of an integrated V2X/LTE system is illustrated in FIG. 1. As shown therein, an LTE communication system 100 includes a plurality of radio communication devices, including a radio access node, such as an eNodeB (base station) 110 and a plurality of user equipments (UEs) including pedestrian-borne UEs 120c, 120d and vehicle-borne UEs 120a, 120b, 120e. As used herein, the term “radio communication device” generally refers to any device capable of wireless communication, including user equipment such as mobile terminals, portable terminals, vehicle borne terminals, and fixed terminals, as well as radio network nodes, such as radio access nodes, base stations, repeaters, etc. A radio communication device that is configured for direct communication as described herein may or may not be part of a radio communication network, such as an LTE network.
Some of the UEs, such as UEs 120a-120d are within range of the eNodeB 110 and communicate with the eNodeB 110 using conventional scheduled resources that are allocated by the eNodeB 110, a radio network controller, or other network node. Some of the UEs, including UEs 120a, 120b, 120c and 120e, communicate directly with one another over a D2D network 140 that does not use scheduled resources controlled by the LTE network 100. Rather, the UEs communicate over the D2D network 140 using contention-based resources that are shared among the UEs in the D2D network 140. Note that the UE 120e is out of range of the LTE network 110, and thus cannot communicate directly with the eNodeB 110.
V2x communications may carry both non-safety-related and safety-related information. Each of the applications and services that utilize V2x communications may have specific requirement sets associated with their use of the technology, such as specific requirements for latency, reliability, capacity, etc.
The European Telecommunications Standards Institute (ETSI) has defined two types of messages for road safety: Co-operative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM).
A CAM message is intended to enable vehicles, including emergency vehicles, to notify other users of their presence and other relevant parameters in a broadcast fashion. Such messages may target other vehicles, pedestrians, and infrastructure, and may be handled by their applications. A CAM message can also serve as active assistance to driving safety for normal traffic. The availability of a CAM message is indicatively checked for every 100 ms, yielding a maximum detection latency requirement of less than 100 ms for most messages. However, the latency requirement for pre-crash sensing warning may be even shorter, e.g., 50 ms.
A DENM message is event-triggered, such as by braking, and the availability of a DENM message is also checked for every 100 ms. The requirement for maximum latency of DENM messages is less than 100 ms.
The package size of CAM and DENM message varies from 100+ to 800+ bytes; the typical size is around 300 bytes. The message is intended to be detected by all vehicles in proximity to the transmitting entity.
The SAE (Society of the Automotive Engineers), another standard setting organization, has defined a Basic Safety Message (BSM) for Dedicated Short-Range Communications (DSRC) with various messages sizes defined.
The BSMs are further classified into different priorities according to the importance and urgency of the messages.
To conform to the Rel 12/13 D2D specification described in 3GPP TS 36.213, it is necessary to transmit a scheduling assignment (SA) packet prior to the transmission of the actual data packet. The SA packet contains information that allows the receiver(s) to find and process the data packet correctly. However, this approach has two major drawbacks: first, it is necessary to dedicate specific resources for broadcasting the SA packets; and second, the latency is increased because it is necessary to decode the SA prior to receiving the data packets in order to obtain the message. Alternative approaches based on blind decoding (i.e., testing all possible control information message hypotheses) of the data packets at the receiving UE result in large computational demands for all but the simplest configurations.
Considering the high peak user capacity targeted by V2X systems, conventional scheduling approaches may incur too much of an overhead cost.
The approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in the Background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the Background section.